The invention is particularly well suited for use in a high capacity plate-type friction draft gear as disclosed, for example, in U.S. Pat. No. 3,150,782 which describes a well known friction clutch mechanism that is comprised of a pair of movable friction plates that protrude from the open front end of the housing of the draft gear, a pair of tapered stationary friction plates located within the housing adjacent and inwardly of the movable friction plates, a pair of friction shoes positioned adjacent and inwardly of the stationary friction plates, and a plunger or friction wedge disposed between the friction shoes and a front follower which is located adjacent the front end of the housing. A one-piece, unitary spring seat is positioned between the friction clutch mechanism and metal coil springs which function to exert a force against the movable friction plates in the direction of the front follower. The friction wedge, as it moves rearwardly of the housing, is designed to wedge the friction shoes outwardly against the stationary friction plates which, in turn, increasingly frictionally engage the movable friction plates to greatly increase the resistance of the draft gear to buff or pull forces being applied against it by the car coupler through the front follower or yoke to which the coupler is attached, as the front follower and protruding ends of the movable friction plats come into contact.
Moderate amounts of wear to the components of the friction clutch mechanism of existing plate-type friction draft gears can cause an abrupt and total loss of dynamic and static frictional capacity which may result in substantial car damage and possibly cause train derailments resulting from exceedingly high dynamic train forces, e.g. about 600,000 pounds, created by unsatisfactory cushioning of the run in and out of free train slack.
Loss of frictional capacity occurs when moderate wear reduces the thickness of the movable and stationary friction plates and the size of the friction shoes and wedge of conventional plate-type friction draft gears. Such wear causes the friction shoes to be expanded and moved outwardly towards the front follower on the wedge by the spring forces which also force the movable friction plates and spring seat outwardly until the movable friction plates simultaneously abut the front follower and spring seat. Continued wear causes the friction shoes to move still further outwardly on the wedge to create a space between the wedge and front follower while the movable friction plates remain in contact with the front follower and spring seat. This causes the train forces to be transmitted directly to the springs through the movable friction plates and spring seat, thereby bypassing the friction clutch mechanism to cause an abrupt and total loss of frictional capacity of the draft gear.
It can be appreciated from the above that it is extremely important to continually monitor the wear of various parts or plates of plate-type friction draft gears presently on the market. This is done by constantly measuring the space between the front follower and adjacent protruding ends of the movable friction plates. The draft gear is rebuilt when the spacing decreases to a certain undesirable level. If not rebuilt at this point, the friction clutch mechanism becomes inoperable for increasing the frictional resistance to movement of the movable friction plates. Thus, the overall high resistance output capability of the draft gear is seriously affected. The invention is directed to an improved friction clutch mechanism for maintaining the draft gear in an operable condition even when the parts of the mechanism become worn to the point of replacement.
Briefly stated, the invention is in a plate-type friction draft gear having a friction clutch mechanism comprising a friction wedge, a pair of friction shoes, a pair of stationary friction plates, and a pair of movable friction plates which protrude from the open front end of the housing and terminate in spaced relation from a front follower which is in contact with the friction wedge. A two-piece split spring seat is provided between the friction clutch mechanism and the spring mechanism that is employed within the housing to exert, through the split spring seat, separate spring forces outwardly against the friction shoes and movable friction plates in the direction of the front follower to maintain the friction clutch mechanism operable by keeping the parts thereof in frictional engagement.
U.S. Pat. No. 3,386,597 shows and describes the use of a split spring seat, but in connection with a completely different type draft gear, which does not utilize movable friction plates for increasing the resistance of the draft gear, and for a totally different purpose; namely, to keep the friction clutch of the draft gear from freezing up or becoming locked against the housing after partial or full compression of the draft gear.